Here you see the entire cochlear spiral. It has been
dissected from the bone of the skull and includes both bony and
membranous labyrinths.
Here you see the entire cochlear spiral. It has been
dissected from the bone of the skull and includes both bony and
membranous labyrinths.
Although there appear to be six or seven openings, they're really one continuous set of channels. The cochlea spirals in and out of the plane of this section, and of course the cochlear duct within it does, too; rather like the ramp going up to the top of a parking garage. The nerve fibers from the organ of hearing and the sites of balance sensation are bundled together as the cochlear branch (CB) and vestibular branch (VB) of the vestibulocochlear nerve (VN). The complete nerve is exiting the image at lower left, carrying sound information and balance information to the brain.
The core of the bony cochlea is the screw-shaped modiulus, a projection formed when the spiraling cavity of the cochlea is hollowed out. The neuron somata of the spiral ganglion (SG) are located along the turns of the modiolus, wound around it.
The membranous labyrinth enclosed inside the cochlea is the scala media or cochlear duct (SM/CD). It houses the actual site of sound transduction. At the apex of the cochlea its two subdivisions (the scala tympani, ST and the scala vestibuli, SV) meet. At their lower end, not seen in this image, they are connected to the vestibule.
The bony labyrinth is filled with perilymphatic fluid. A wave of disturbance set up in the perilymph at the the vestibule can travel up the spiral via the scala vestibuli; at the helicotrema the impulse is passed to the scala tympani and it then moves back down the spiral. Disturbances in the perilymph can be transmitted to the endolymph enclosed within the cochlear duct, or scala media, that lies between them.
Inner ear; paraffin section, H&E stain, 20x
